1. Field of the Invention
The present invention relates to a substrate for an electro-optical device, and more specifically, the invention relates to a color filter substrate for a transflective liquid crystal display, a color filter substrate for a multi-domain vertical alignment mode liquid crystal display (MVA-LCD), and a method of manufacturing the same. Further, the present invention relates to an electro-optical device utilizing the color filter substrate, and an electronic apparatus provided with the electro-optical device.
2. Description of the Related Art
Liquid crystal displays are commonly mounted in electronic apparatuses such as cellular phones and portable personal computers. In particular, transflective liquid crystal displays capable of displaying images in both a transmissive display mode and a reflective display mode have been widely used.
The transflective liquid crystal display mainly has a structure in which a liquid crystal layer in a twisted nematic (TN) mode is interposed between a first substrate, on which a first transparent electrode is formed, and a second substrate, on which a second transparent electrode is formed, which faces the first substrate. A light reflecting film forming a reflective display region is formed on the first substrate in a pixel region where the first transparent electrode faces the second transparent electrode. A region corresponding to an aperture provided in the light reflecting film is a transmissive display region. A polarizer, a retardation film, etc., are arranged outside each of the first substrate and the second substrate. Further, a backlight unit for transmissive display is arranged outside the polarizer on the first substrate side on which the light reflecting film is formed.
In the transflective liquid crystal display, among light components emitted from the backlight unit, light components incident on the transmissive display region are incident on the liquid crystal layer from the first substrate side, are light-modulated in the liquid crystal layer, and are emitted from the second substrate side as transmissive display light, thereby displaying images (a transmissive display mode).
Further, among external light components incident from the second substrate side, light components incident on a reflective display region reach the light reflecting film through the liquid crystal layer, are reflected by the light reflecting film, and are emitted from the second substrate side after again passing through the liquid crystal layer as reflective display light, thereby displaying images (a reflective display mode).
Color filters for reflective display and color filters for transmissive display are formed on the first substrate in the reflective display region and the transmissive display region, respectively. Therefore, color display can be performed in both the transmissive display mode and the reflective display mode.
As mentioned above, when the liquid crystal layer modulates light, changes in the polarization state are based on a function of the product (retardation: Δn·d) of a refractive index difference Δn and a liquid crystal layer thickness d. Therefore, when the refractive index difference Δn and the liquid crystal layer thickness d are made appropriate, it is possible to display images with improved visibility. However, in the transflective liquid crystal display, the transmissive display light is emitted after passing through the liquid crystal layer once whereas the reflective display light passes through the liquid crystal layer twice. Therefore, it is difficult to simultaneously optimize the retardation in both the transmissive display light and the reflective display light. That is, when the thickness d of the liquid crystal layer is set so that the visibility of the liquid crystal display is improved in the reflective display mode, display in the transmissive display mode is sacrificed. To the contrary, when the liquid crystal thickness d is set so that the visibility of the liquid crystal display is improved in the transmissive display mode, display in the reflective display mode is sacrificed.
In consideration of the above problems, a transflective liquid crystal display having a structure in which the thickness of the liquid crystal layer in the reflective display region is smaller than the thickness of the liquid crystal layer in the transmissive display region is disclosed. Such a liquid crystal display is referred to as a multi-gap type liquid crystal display.
The multi-gap type transflective liquid crystal display can be realized by forming an overcoat layer on the reflective display region, specifically, on the color filters for reflective display in order to control the thickness d of the liquid crystal layer. At this time, the overcoat layer is not formed on the color filters for transmissive display. In short, the thickness d of the liquid crystal layer in the transmissive display region increases by such an extent that the overcoat layer is not arranged compared with the reflective display region. Therefore, it is possible to optimize retardations with respect to both the transmissive display light and the reflective display light, and thereby display images with improved visibility in both the transmissive display mode and the reflective display mode.
In the multi-gap type transflective liquid crystal display, the thickness d of the liquid crystal layer is optimized in the reflective display region and the transmissive display region by forming an overcoat film on the substrate.
However, as mentioned above, in the multi-gap type transflective liquid crystal display, the overcoat film is formed under the pixel electrode (the transparent electrode) in order to control the thickness d of the liquid crystal layer in the transmissive display region and the reflective display region. That is, in the reflective display region, the overcoat layer is formed on the color filters for reflective display. Therefore, the pixel electrode (the transparent electrode) is formed on the overcoat layer. In the transmissive display region, the overcoat layer is not formed. Therefore, the pixel electrode (the transparent electrode) on the color filters for transmissive display is formed without the overcoat film. Even when the overcoat film is formed in the transmissive display region, the overcoat film having a substantially smaller thickness than the thickness of the overcoat film in the reflective display region is formed. Tapers are formed in the overcoat film in the display region in order to change the thickness of the overcoat layer.
In general, the taper of the overcoat film in the display region of the multi-gap type transflective liquid crystal display needs to be significantly inclined with respect to the surface of the overcoat film in the reflective display region in order to improve the contrast. This is because the thickness d of the liquid crystal layer positioned on the taper of the overcoat film, i.e., the surface of an inclined plane, significantly affects the contrast of the liquid crystal display.
As mentioned above, the multi-gap type transflective liquid crystal display is optically designed by examining the optimal value of the retardation. That is, since the thickness d of the liquid crystal layer significantly affects the value of the retardation, a panel is designed so that the optimal value of the thickness d of the liquid crystal layer is obtained in the reflective display region and the transmissive display region. Therefore, it is necessary to pattern the overcoat film so that the taper of the overcoat film is significantly inclined and that a difference between the actual thickness d of the liquid crystal layer and the optimal value thickness d of the same is as small as possible.
However, in the liquid crystal display, the transparent electrode generally tends to be arranged on the overcoat film. The transparent electrode is continuously formed on both the reflective display region and the transmissive display region over other adjacent dot regions. That is, the transparent electrode is an electrode wiring for driving liquid crystal molecules.
In a case where the taper of the overcoat film is significantly inclined, when the transparent electrode is formed using a sputtering method, etc., it is difficult to form the transparent electrode because the surface of the taper is significantly inclined. Therefore, the transparent electrode may be disconnected in the significantly inclined taper. This problem occurs in, particularly, an electrode wiring laid-around portion of the taper of the overcoat film formed in a region outside the display region. The electrode wiring laid-around portion is formed on the substrate for the liquid crystal display on the outer periphery of the substrate in order to electrically connect the transparent electrode corresponding to the display pixel to a driving IC. When disconnection occurs in the electrode wiring laid-around portion, signals are not transmitted to one entire scanning line, resulting in inferior display.